Sound record



May 7,1940. J. Q. BAKER 2.1994606 SOUND RECORD Original Filed May 28, 1936 t 'iv 7 Q 3% f? 1? I I 4 I 10 I v I I {z-{llzlllllllllllll l I u A 411 IN VEN TOR Paenaa May 1, 1940 UNITED S TES SOUND RECORD Judd 0. Baker, Westmont, N. 3., assignmto RadioCorporation of America, a corporation of Delaware Original application May 28, 1936, Serial N0.

82,375, now Patent .No. 2,102,776, dated December 21, 1937.

Divided and this application August 31, 1937, Serial No. 161,759

3 Claims.

The present invention relates to a sound record and more particularly to a sound record of the photographic type provided with ground-noise reduction, this application being a division of my application Serial No. 82,375, filed May 28, 1936,

now Patent No. 2,102,776, granted December '21, 1937.

The recording of sound on film by what is known as the variable area methodhas been known for a number of years and is described, for example, in Fritts Patent No. 1,203,190. In the reproduction of the earlier variable area sound records, as well as variable density sound records, there is produced what is known as ground noise." due to imperfections in the film and to noise produced in the photo cell, and in these earlier films the volume of this noise was constant as the average light transmission was constant and, accordingly, it was very objectionable at low sound volumes. It was accordingly proposed as, for example, in Robinson Patent No. 1,854,159 to reduce the transparent area of the positive film at low sound amplitudes thereby decreasing the ground noise as the volume of sound was decreased and correspondingly improving the quality of the sound at low amplitudes.

It was proposed in McDowell Patent N0. 1,855,197 to use a shutter in the sound recorder to cover, and thereby render transparent, the unused portion of the sound negative which in turn rendered the corresponding portion of the positive film opaque in order to reduce ground noise. My present invention is an improvement on the film produced by the said McDowell apparatus.

One object of my invention is to provide a sound record which is symmetrically arranged in relation to the sound track area.

Another object of my invention isto provide such a sound record having ground-noise reduction.

Other and incidental objects of my invention will be apparent to those skilled .in the art from a reading of the following specification and an-ina spection ofthe accompanying drawing in which Figure l is a schematic representation of a sound recording apparatus built in accordance with my invention,

Figure 2 is a. horizontal section through my improved optical system and shutter arrangement,

Figure 3 is a vertical section thereof,

Figure 4 is an end view looking from the right hand side of Figures 2 and 3,-

Figure 5'shows details of the construction,

(Cl. 274-4L6) Figure 6 shows a positive print of my improved sound record.

Referring to Fig. 1, the sound recording microphone is indicated at I and the microphone amplifier at 2. From this microphone amplifier a portion of the current is fed to the main recording amplifier 3, which in turn actuates the galvanometer 4, thereby causing the galvanometer mirror 5 to oscillate about a horizontal axis.

A portion of the output from the amplifier 2 is fed to the groundnoise reduction amplifier 5, which may be constructed in accordance with the said McDowell patent. This amplifier 6 amplifies the current fed to it, then rectifies the amplified current and passes the rectified current through a low-pass filter, thus providing a variable direct current output, tlielnstantaneous value of which corresponds to the-average value of the sound input to the galvanometer. Such a current is commonly termed an envelope current, as it corresponds to the envelope of the sound waves.

In the. recorder, light from an exciter lamp 1 is passed through a condenser lens 8 and an aperture plate 9 to the lenses l0 and H. These lenses l0 and Il concentrate the light on the galvanometer mirror 5 and also serve to focus an image of the aperture 8 2 in the plate 9 on the slit plate 83. This slit plate is provided with a narrow slit Hi which serves to select the desired portion of the image 92', which is then focused on the film 55 by the lenses l6 and ll. As shown in the drawing, the aperture. I2 is in the form of an elongated rectangle with two triangular extensions on one side and a smaller rectangularextension on the other side. When this aperture is imaged on the plate l3, as indicated at E2, the triangular portions fall on the slit l8 and produce two areas of illumination of the slit. when the galvanometer mirror 5 is oscillated about a horizontal axis, these triangular areas move up and down across the slit l4, thereby causing the slit to intercept portions thereof oi difierent lengths and correspondingly producing two separated sound records, each corresponding to the sound being recorded. Light from the rectangular extension in the aperture i2 is deflected by the prism 18 and is again reflected by the prism it onto the screen 20, where the movement of this portion of the spot of light permits the operator of the apparatus to see the manner in which the galvanometer is operated.

Current from the ground-noise reduction amplifier 6 is passed to a magnetic means 2!, which may be of any desired type, where it is caused to deflect a movable member 22 in accordance with the amplitude of the envelope current. As the member 22 is deflected it pulls upon a flexible resilient member 23, thereby causing the shutters 24 and 25 to move about the pivots 26 and 21 against the tension of the spring 28. It will be apparent that the amplifier unit 6 may be so connected as to cause an increase in the envelope current when there is a decrease in the output of the'amplifier' 2, thereby causing the shutters 24 and 25 to be moved toward each other and masking oil a corresponding portion of the aperture 2. Alternatively, the shutters 24 and 25 may be mechanically adjusted to remain in their most nearly closed position and when there is an increase in output from the microphone the output from the amplifier and rectifier 6 would then be so connected as to cause the shutters to be opened by the increasing current.

I prefer, however, to have the shutters mechanically adjusted so that when their circuit is open they are in the position shown in Fig. l; to adjust the amplifier and rectifier 6. so that when the circuit is closed, the shutters 24 and 25 are pulled to their closed position when there is no input; and when modulation is applied to the amplifier 2, and the rectifying amplifier 6 to cause the current through the magnetic means 2| to decrease, thereby permitting the shutters to open in accordance with the amplitude of the sound to berecorded. It will be apparent that the selection of any one of these three methods can be accomplished by merely a reversal of connections either between amplifier 2 and the rectifying amplifier 6, between amplifier 6 and the magnetic means 2|, or of magnetic means 2| to the arm 22. Similarly, if it is desired to cause a decrease in the output of the amplifier 6 or an increase in the output of the amplifier 2, it is necessary that the output of the amplifier 2 increase the negative grid bias in the rectifying amplifier 6, while to produce the opposite result,

the connections are so made-as to cause a decrease in the grid bias.

The aperture plate 9 is located quite close to the shutters 24 and 25 and when the shutters are in the closed position, i. e., when there is no sound being recorded, each covers approximately one-fourth of the aperture I2. When the image of this covered aperture is projected on the slit plate l3, only narrow tips of the image |2.' coincide with the slit, thereby producing only a very narrow record such as indicated at 30 in Fig. 6. When, however, modulation is applied to the amplifier 2, the shutters 24 and 25 are withdrawn toward the position shown in Fig. 1, a distance corresponding to the amplitude of the sound to be recorded, and when the shutters are completely withdrawn, for recording maximum amplitude, the image I2 on the slit plate l3 presents the appearance shown in Fig. 1. Since Fig. 6 shows the positive film which is adapted for the reproduction of sound and the positive is a print from the negative produced in the recorder, the portions which are clear in the positive and shown unshaded in Fig. 6 will be dark in the negative.

This positive sound record is carried as usual on a film base and includes a sound track area having the parallel margins 66 and 6|. These margins define an area having some width approximately the same as the length of the scanning line used in the reproducer, and the portion between these margins is customarily referred to as the sound track. Within this sound track area which extends longitudinally of the 2,1ee,coc

film there are three exposed areas arranged symmetrically about the longitudinal axis 62' of the sound track defined by the margins 60 and 6|. This axis 62, of course, lies midway between the margins 6|! and 6|. The exposed area 65 which has its edges contoured in accordance with the sound waves, is symmetrical about the axis 62. It will be noticed that the peaks 3| and the valleys 32 in this axial area extend equal disstances from the margins of the axial area undemodulated as shown at the top and bottom of the figure. If the areas of these sound waves are averaged, it will be found that the axial area has a constant average width, and if it were applied alone to a transparent background, the

record would have a uniform average transmission longitudinally irrespective of the modulation. This uniform average transmission is undesirable since at points of no sound the background noise would be noticeable while at points of loud sound the background noise would be obscured by the sound. In order to eliminate the background noise the dark marginal areas 63 and 64 are provided, the inner edges of which follow the contour of the peaks 3| of the sound'waves and which, therefore, when there is little or no sound, decrease the light transmission and correspondingly decrease the ground noise. It will be apparent from this that the contour of the inner edges of the marginal portions 63 and 64 will be in accordance with the volume of the sound and will correspond to the envelope of the sound waves. Likewise, in order to follow the envelope of the sound waves, since the edges 60 and 6| are straight, the width of the mar-- ginal area 63 and 64 will vary inversely with the amplitude of the sound waves.

The negative from which the print shown in I Fig. 6 is made and which has exposed areas corresponding to the clear areas in Fig. 6 is pro- Y modulation, a negative record will be producedfrom which a positive may be printed having the appearance shown in Fig. 6, from which it will be apparent that the record has an outer envelope corresponding with the envelope of the voice currents and an inner outline corresponding with the sounds themselves, the outer envelope being produced by the shutter and the inner outline being produced by the galvanometer. It will be apparent that each of the halves of this record corresponds with the McDowell record but that two records are symmetrically arranged with relation to the sound track, thereby preventing the cutting oif of peaks at high amplitudes if the reproducing aperture is slightly out of alignment by preventing the cutting out of the sound under similar circumstances at extremely low amplitudes which might follow with such sound records, as for example that of Hanna Patent No. 1,888,724.

The specific shutter mechanism is described in greater detail and claimed in the concurrently filed applications of myself and Cecil N. Batsel, now Patent No. 2,102,777, and the application of optical system including the condenser 8, the

lens it, and the intervening'shutter mechanism is mounted. On this is mounted an appropriate carriage it. As shown in Fig, 4, this carriage is mounted for lateral movement on the member 59, being shifted by the screw 43 provided with the jam nut it and being held firmly in position by the compressionspring it which produces a pressure opposing that exerted by the screw 53.

This carriage d2 includes a cylindrical upper portion at in which the barrel fill of the optical system is fitted.

In order to position the optical system with the aperture 52 accurately parallel to the slit I5, the'optical barrel is slitted at 68 and into this slit is fitted an eccentric pin 88 on a screw 50. It will be apparent that rotation of the screw 56 will cause the pin 9 to move laterally of the member 65 and to thereby rotate the barrel together with the aperture plate 9. The barrel may not only be rotated but may be slid longitudinally within the limits prescribed by the slots 58 and it can then be clamped in place by the screw at, which passes through the slit ring 52 and which forms a portion of the member 85.

As shown in Fig. 2, the shutters 24 and 25 are pivoted on the knife edges 25 and 21, being held thereagainst by the spring 28. These shutters 2d and 25 are adiustably secured on the arms 53 and 55 by the screws 55 and 56 in order that they may be adjusted to the proper distance fromthe aperture plate 9. It will be apparent that, although the ends of the shutter blades must clear the aperture plate t, they must, at the same time, be so close thereto that a properly focused image'of the edges of the shutters will be formed on the slit plate it in the same focal plane with the image of the aperture l2. The individual shutter blades are adjustable laterally by means of screws 51 and at as shown in Fig. 5, these screws passing through v-shaped blocks 59 and $9, Figs. 3 and 5, which are held into the correi shaped slideway 5i by the spring members 62. It will be apparent that rotating the screws 51 and 58 will shift the blocks 59 or 80 longitudinally in the guideway, therebyshiiting the pivots of the shutters and correspondingly shifting the opposite ends of the shutter blades in the opposite direction to the movement of the pivots.

As before described in connection with Fig, i,

a resilient member 23 is connected from the arm 22 to the arms supporting the shutters and when this arm is actuated by the magnets the shutters are pulled closer together or moved farther apart, as the case may be.

In the preferred form of the invention, as shown in Figs. 2 and 5, the arm 23 is provided with a rectangular armature 63 as shown in dotted lines in Fig. 3, and moves in a plane passing through the axis of the lenses between the poles of the pairs of magnets St and 55. The coils of'the several magnets 64 and t5 are connected to the ground noise reduction amplifier 6 and in such a manner that the pairs of poles longitudinally of the device are or opposite polarity, thereby causing movement of the arm 23 in accordance with the energization of the magnets and correspondingly moving the ends of the shutters 24 and 25.

Having now described my invention, I claim:-

1. A sound record having thereon a sound track area having parallel margins, a sound wave record located midway between said margins and having an average width substantially half of r the distance between said margins, the said sound wave record having sound wave images on each of its edges, 9. continuous sound-amplitude record on each side of said sound wave record, said sound amplitude records following the peaks of the sound wave record and substantially filling the spaces between said peaks, and said parallel margins.

2. A sound record. as defined in claim 1 wherein the sound wave record and the sound amplitude record are substantially opaque and the intermediate area is substantially clear.

, 3. A sound record as defined in claim 1 wherein ,5

the sound wave record and the sound amplitude record are substantially clear and the intermediate area is substantially opae. 

